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DELINEATION OF THE OUTER
LIMITS OF THE CONTINENAL
SHELF BASED ON SEDIMENT
THICKNESS
(CHAPTER 8)
Article 76, paragraph 4 a)
“For the purposes of this Convention, the
coastal State shall establish the outer edge
of the continental margin wherever the
margin extends beyond 200 nautical miles
from the baselines from which the breadth
of the territorial sea is measured, by either:
Article 76, paragraph 4 a)
(i) a line delineated in accordance with
paragraph 7 by reference to the outermost
fixed points at each of which the thickness
of sedimentary rocks is at least 1 per cent
of the shortest distance from such point to
the foot of the continental slope; or
Determination of the outer edge of the
continental margin by sediment thickness
Baseline
Continental margin
Foot of
slope
1 % of distance
to foot of slope
Crystalline continental crust
Oceanic crust
Nautical mile( M )
0
100
200
300
400
STATEMENT OF UNDERSTANDING
CONCERNING A SPECIFIC METHOD
TO BE USED IN ESTABLISHING THE
OUTER EDGE OF THE CONTINENTAL
MARGIN
Final Act of third UN Conference- Annex II
Final Act - Annex II
A request from the Third Conference to the
CLCS to let itself be governed by a set of
special rules for the coastal States in the
southern part of the Bay of Bengal.
These rules aim to compensate for the
exceptional shape and sediment distribution
of the continental margin in this region.
Final Act - Annex II (continued)
The essence of these special rules is that
paragraph 4 (a) (i) and (ii) of article 76 is
replaced by a provision that the outer edge of
the continental margin may be established by
straight lines not exceeding 60 nautical miles
connecting fixed points at which the
sediment thickness is not less than 1
kilometre.
Application of Gardiner Rule
“A coastal State that intends to apply this provision
will have to document the position of the foot of the
continental slope and the thickness of sediments in a
seaward direction from it.”
CLCS/11, paragraph 8.1.4
Application of Gardiner Rule (cont)
Implementation of provision involves:
- identification of the sediment/basement interface
- the calculation of sediment thickness
- identifying the variability of sediment distribution
CLCS/11, paragraph 8.1.4
Definition of sediment thickness
“The sediment thickness at any location on the
continental margin is the vertical distance from the
sea floor to the top of the basement at the base of the
sediments, regardless of the slope of the sea floor or
the slope of the top basement surface.”
CLCS/11, paragraph 8.1.8
Definition of sediments
“.... The sediments may comprise a pre-rift and a synrift sequence overlaid by a post-rift sediment wedge
(fig. 8.1). If syn-rift or pre-rift sediments are
preserved below the post-rift unconformity, these may
be included in the sediment thickness estimation.”
CLCS/11, paragraph 8.2.16
Definition of sediments (continued)
CLCS/11, Fig. 8.1
Definition of sediments (continued)
The sediments may include interbedded volcanic
material like volcaniclastics deposits and lavas.
See CLCS/11, paragraphs 8.1.6, 8.2.18 & 8.4.3
Fig. 10
Relevant geophysical data
Primary data:
- Seismic reflection data (multi-channel superior)
- Seismic refraction/wide angle reflection data
- Well data
Complementary data:
- Gravity field data
- Magnetic field data
Well data sources
• Petroleum industry exploration wells,
especially deep water wells
• Wells from the Deep Sea Drilling Program
• Wells from the Ocean Drilling Program
Depth conversion
”The estimation of sediment thickness requires the
depth conversion of the interpreted profiles and maps.
This depth conversion of the geophysical data should be
documented by the relevant database and the description
of the method applied.”
CLCS/11, paragraph 8.3.1
”Depth conversion of seismic data requires velocity data
to build a velocity model for the sediment wedge. Such
velocity models describe the vertical and/or lateral
variation in seismic propagation velocities within the
sedimentary sequences.”
CLCS/11, paragraph 8.3.9
Minimum requirements
• Document required sediment thickness at
fixed points at a maximum spacing of 60 M
• For each fixed point, document the
geological interpretation and present both
the original and the interpreted data
• For each fixed point, document the method
for depth conversion and the parameters
involved
• Document the expected ranges of error
Selection of fixed points
• The coastal State may choose the outermost
location where the required sediment
thickness occur within and below the same
continuous sedimentary apron, irrespective
of lateral variations in sediment thickness
• Document the continuity between the
sediments at those points and the sediments
at the foot of the continental slope
(see CLCS/11, paragraph 8.5.3)